1. Field of the Invention
This invention relates to mobility canes for sightless persons in general, and to such canes incorporating ultrasonic obstacle detection apparatus, in particular.
2. Description of the Prior Art
Mobility canes incorporating range extending devices for sensing potential obstacles to blind, ambulatory users of such canes have been disclosed in the prior art.
In U.S. Pat. No. 3,546,467 to BENJAMIN, JR., et al., a relatively costly and complex mobility cane utilizing a plurality of aesthetically objectionable, object detecting, coherent light (laser) sensor pairs, is described. Highly directional transmitting and receiving sensors are mounted in a spaced relation on the cane shank. The ability to adjust the object sensors to the desired maximum object detection range is dependent upon the ability to mechanically set the angular position of each sensor with respect to said cane shank. The protective zone provided to a cane user with this arrangement is quite limited in that an object must actually intersect a relatively narrow light beam in order to be detected. Also, objects lower than the maximum laser sensor object detection height will be detected closer to a cane user than more elevated objects, and said user may not be able to react in sufficient time to avoid object contact.
U.S. Pat. No. 2,496,639 to RICHARDT, JR., et al., discloses a mobility cane employing a pair of ultrasonic energy transmitting and receiving piezoelectric transducers. This particular cane is less complex and has a greater protective zone for a transducer pair than that of the above-mentioned BENJAMIN, JR., et al. cane; however, it suffers all of the other shortcomings of said BENJAMIN, JR., et al. mobility cane.
Ultrasonic range finders for detecting the presence of, and the distance to, a subject to be photographed have also been disclosed in the prior art. In U.S. patent application Ser. No. 3,371, filed Jan. 15, 1979, by J. MUGGLI, an ultrasonic range finder having a combination transmitting and receiving, capacitance type, electrostatic transducer, is incorporated in a photographic camera for the purpose of determining the distance to a subject and then causing the adjustable focus lens of said camera to be focused in accordance with a signal representative of subject distance derived by said range finder.